Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually Opal is formed. The tightly packed spheres of silica in opal refract light passing through it, creating a play-of-colour that is fascinating and highly sought after in precious opal.
The physical and optical properties of cultured opal are almost identical to those of natural opal. The main difference is that the opal has been impregnated with an extremely hard polymer resin which permanently binds the silica spheres together. The resulting opal is 80-90% pure opal silica exhibiting a play-of-colour and vibrancy that equals the most prized of all precious opals. Its treatment results in a generally much stronger and more stable gem than natural opal, making it less vulnerable to heat, cracking or crazing. Cultured opal is a form of solid opal not to be confused with ‘doublets’, ‘triplets’, ‘opaline’, ‘reconstituted opal’ or other such imitations.
Natural Opal: SiO2.nH2O
Cultured Opal: SiO2.nH2O + polymer
It can take between one and two years to grow a solid opal, so it is not an entirely inexpensive alternative to buying one that has formed naturally. However vivid flashes of colour are not easily found in the naturally occurring variety as it is so rare. Natural opals with a strong play-of-colour are usually either too expensive or too difficult to finder most to hope to acquire. As cultured opals are more affordable, they are a popular option and benefit from having the colour of a far more expensive gemstone.
See our new collection of cultured opals.